I love 1/4-20 sockets. Attach my camera to a flash bracket? Yep. Attach an eyebolt to attach a carabiner to attach a neck strap? Yep. Attach a hand strap or a 40mm, 80mm, or 200mm Arca Swiss plate. Yep. Yep, Yep and Yep. There's nothing stopping a photographer from permanently attaching an Arca-Swiss plate to the bottom of a camera body with a bit of cyanoacrylate or some screws if it makes better photographs. For me…
I think you're missing the point. If camera manufacturers just molded an Arca Swiss dovetail into the bottom edge of their cameras, then you could have both solid, easy QR compability and the 1/4 socket--simultaneously. The way it works now, you have to use the 1/4 socket to get QR compatibility.
That said, from an engineering perspective the long term durability of a plastic molded dovetail when clamped in a metal Arca Swiss clamp might be a challenge because the Arca Swiss system is not designed around that degree of dissimilarity of material hardness (not that I have anything against plastic). One of the characteristics of Arca Swiss connections is that they are not based on a formal standard and this leads to minor dimensional variability among components that is mitigated by clamping the clamp tighter or buying components from a company like Arca-Swiss at the prices their products command.
Potential durability aside, a molded in dovetail would increase the bulk of a camera and generally the trend seems to be away from camera bulk all things being equal. While a molded in adapter might increase stability in some cases, in others it would decrease it. Setting a camera on a table is an obvious case. Any other mounting is also going to be through a longer lever arm and with a higher center of gravity.